The exemplary embodiments relate to a technique for varying gradation attributes of an image signal in accordance with characteristics of a displayed image.
In a related art image display system, input-output attributes indicating variations in brightness of displayed images with respect to image signals representing input images (input image signals) are controlled to obtain a desired image quality of the displayed images. In a related art method to control the input-output attributes, characteristics of the input images are detected to dynamically vary gradation attributes of brightness signals constituting the input image signals in accordance with the detected characteristics of the input images. (For example, see: Japanese Patent Application Publication No. 2003-110878; Japanese Patent Application Publication No. 2003-337580; Japanese Patent Application Publication No. 2003-259154; Japanese Patent Application Publication No. 2003-298974; Japanese Patent Application Publication No. 2003-46807; Japanese Patent Application Publication No. 2002-359754; and Japanese Patent Application Publication No. 10-248024).
According to the related art method, the gradation attributes are varied in accordance with the maximum brightness, the minimum brightness, the average brightness, the brightness histogram, and the like, in the brightness signals constituting an input image on one frame. Since attributes of high gradation are controlled according to the maximum brightness, and attributes of low gradation are controlled according to the minimum brightness, the minimum brightness is not reflected in the control of high gradation, and the maximum brightness is not reflected in the control of low gradation. Realistically, however, the brightness of high gradation affects the attributes of low gradation and the brightness of low gradation affects the attributes of high gradation. Thus, the related-art method is insufficient to appropriately control gradation attributes in accordance with the characteristics of input images.